Current research comprises two quite different areas: cooperative nonlinear
optics and ultrahigh-resolution laser spectroscopy of point defects in
wide-bandgap semiconductors. Cooperative nonlinear optics focuses on the
interaction of light with clusters of neighboring impurities in solids (or
colliding atoms in gases).

Near-neighbor atoms are coupled with clusters of neighboring impurities in
solids (or colliding atoms in gases). Near-neighbor atoms are coupled
oscillators which exhibit nonlinear emission or absorption at unexpected
frequencies in a manner quite different from conventional nonlinear optics. We
study coupled pairs and trios of atoms in rare-earth-doped solids, and have
demonstrated several upconversion lasers and novel nonlinear devices based on
them.

Upconversion lasers are distinctive in providing output frequencies higher than
their excitation or pump frequency. Bistable devices based on cooperative
interactions should also exhibit unusually low power requirements; however,
fundamental aspects of pair interactions with light are of principal concern.
Hence we are also currently developing a rigorous quantum theory for avalanche
upconversion, and exploring the implications of spatial coherence in such
processes for population pulsations and possibly chaotic behavior.

Nonlinear spectroscopy emphasizing hole-burning, four-wave mixing and coherent
transient techniques are used to study the physical and electronic structure of
point defects and dopants in solids. Centers of interest in diamond and
ALxGA1-xN influence semiconducting properties in important ways. Alternatively,
they may be candidate centers for short-wavelength tunable injection lasers and
detectors.

However, very little detailed knowledge is available for many of the centers in
these novel electronic materials and the materials themselves are rare.
Although our primary interest is in precision spectroscopy, we have therefore
found it necessary, for example, to grow our own CVD diamond films in order to
prepare spectroscopic samples with desired concentrations of impurities or color
centers, using particle beams and annealing procedures.

Coherent optical spectroscopy with both femtosecond pulses (giving rise to
photon echoes) and continuous-wave lasers (cw four-wave mixing and phase
conjugation) is then used to determine energy levels, decay times, and symmetry
information about simple point defects. The objective is to furnish the
necessary knowledge base for applications of the type mentioned above.

Stephen Rand received his Bachelor's Degree in Science (Physics) from McMaster
University in Hamilton, Ontario, and his M.Sc. and Ph.D. (Physics) at the
University of Toronto. In 1989 he was a CNRS invited professor at the
University of Grenoble. In 1994 he was a Fulbright scholar and a College de
France visiting professor. He is Topical Editor for the Journal of the Optical
Society of America B.